1. Field of the Invention
This invention relates to an apparatus and method for removing undesirable material from the edge of an object, and more particularly, this invention relates to the removal of undesirable material from the edge of an object during rotation of the object by applying a solvent for removal of the undesirable material to a flat surface adjacent the edge.
2. Description of the Prior Art
During the processing of semiconductor devices, it is necessary to apply certain liquids, for example, resist, developers, and cleaning solutions to the wafer on which the semiconductor device is located. Generally, in order to apply these liquids, the wafer which has a substantially circular shape, is spun at high speed and the liquid is applied to the surface of the wafer. The apparatus for accomplishing the application of liquids to semiconductor wafers is known as a spinner. One type of spinner receives the semiconductor wafer from an air track mechanism. The air track mechanism moves the slice onto the chuck of the spinner. A vacuum is then applied through the upper surface of the chuck for frictionally engaging the wafer therewith. The vacuum overcomes the support provided by the air jets of the air track mechanism, thereby lowering the wafer and engaging it with the upper surface of the chuck. The chuck is, for example, then lowered into a chamber for application of fluid to one of the parallel surfaces of the wafer.
Generally a semiconductor wafer is comprised of, for example, a slice of monocrystalline silicon. The wafer has two parallel flat surfaces and an outer thin, convex edge which forms the perphery connecting the two surfaces. The outer edge can be generally circular, although a cut out region can be provided, which is generally referred to as a flat. The flat provides orientation information for various machinery within the semiconductor integrated circuit production environment When the spinner is prepared to apply the liquid to the semiconductor wafer, the chuck is rotated at high speed. The speed is on the order of 2000 to 6000 rpm. The axis of rotation is substantially perpendicular to the parallel surfaces of the wafer and concentric with the outer edge. Further, it is generally desirable that the axis of rotation of the chuck be approximately coincident with the center of the semiconductor wafer so that the application of the liquid to the semiconductor wafer can be at the center of the wafer in order to provide a coating across the entire surface, including the center thereof, without any gaps.
The application of liquid to semiconductor wafers is performed during the processing of the wafers to form integrated circuits thereon. The process includes many steps during which it is desirable to apply liquid to the surface of the semiconductor wafer where the structures forming the integrated circuits are located. At least some of the steps are to provide for coatings, for example, resist. The resist, which can be, for example, photoresist, ebeam resist x-ray resist, etc., of the positive or negative type, is applied as a liquid which is dried on the semiconductor wafer to form a coating thereon. The resist in the form of liquid is applied to the semiconductor wafer while it is being spun on the chuck. Although a coating is left on the surface of the semiconductor wafer to which the liquid is applied, the liquid moves outward through centrifugal force and onto the edge. At least some of the liquid remains on the edge to form deposits of resist on the edge. These deposits are generally referred to as edge beads. The edge beads are undesirable in that as the wafer is processed, various mechanisms and possibly edges of the air track can come into contact with the edge of the wafer and thereby causing the resist to flake off, forming particulate matter. It is well known that particles in the ambient environment about a semiconductor wafer are highly undesirable because the particles can cause defects in the integrated circuits they contact and adhere to.
Although a semiconductor wafer is shown herein, the present invention can be utilized with any object having a flat surface adjacent a convex edge having material thereon which it is desired to remove.
None of the known prior constructions shows the removal of undesirable material from the edge of an object having a flat surface adjacent a convex edge by the application of a solvent fluid to the flat surface by contact or gravity feed and its movement along the flat surface and out onto the convex edge by centrifugal force.